This is not really a bug. By default all pings and notifications go out immediately after posting. You just need to enable asynchronous pings on General settings > Features and set up the scheduler.

http://manual.b2evolution.net/Scheduler

Maybe we should drop pings and notifications if post date is in future...

For me it's a bug. If the date is in future, notification should not happen in any case.

Moreover I got this problem when attaching an image in a post.

I begin to write a post. I set the title, I set the date in the future, the visibility to published. I click "Add/Link files" and then the notification was sent even if the post was not finished (I did not click the save button

http://slamp.free.fr/b2evo/bugNotification.png